1. Field of the Invention
The invention relates to a fuel cell system, and an operation method for the fuel cell system. Particularly, the invention relates to a failure detection regarding a circulation pump for circulating the fuel gas.
2. Description of the Related Art
In recent years, fuel cell that generates electric power through the use of a fuel gas containing hydrogen and an oxidizing gas containing oxygen are drawing attention. A fuel cell system having such a fuel cell includes a fuel gas supply channel that supplies the fuel gas to the fuel cell, a fuel gas circulation channel that circulates the fuel gas discharged from the fuel cell by returning it to a fuel gas supply channel for reuse, a circulation pump provided on the fuel gas circulation channel so as to circulate the fuel gas, etc. Among these gas channels, the channels in which the fuel gas circulates are called circulation system channels as well.
A fuel cell system as described above, at the time of startup, performs a pump driving detection in which the driving of the circulation pump is attempted and it is detected whether or not the circulation pump is driven (Japanese Patent Application Publication No JP-A-2004-172025). In this pump driving detection, if it is detected that the circulation pump fails to be driven, it is determined that the circulation pump has a breakdown, and a measure, for example, stopping the power generation, is taken.
In the fuel cell, water is produced by an electrochemical reaction during power generation, and the reaction-produced water circulates in a circulation system channel, and sometimes remains in the circulation pump. If, with water remaining, the outside air temperature falls below freezing point and the operation of the fuel cell system is stopped for a certain amount of time, the water remaining in the circulation pump freezes. In that case, there is risk of the circulation pump failing to be driven.
Therefore, if, at the time of starting the fuel cell system, the pump driving detection is performed and the circulation pump fails to be driven, a case is conceivable in which the circulation pump fails to be driven because of the freezing as well as a case where the circulation pump fails to be driven because of a breakdown. Hence, as for the pump driving detection, there is risk of falsely determining that the circulation pump has a breakdown in the case where the circulation pump fails to be driven due to freezing, and actually does not have a breakdown. In consequence, there is risk of bringing about an inconvenience in which the power generation has to be stopped although the circulation pump actually does not have a breakdown.